Voltage generation utilizing piezoelectric effects



Aug. 13, 1968 H. w. SCHAFFT 3,397,323

VOLTAGE GENERATION UTILIZING PIEZOELECTRIC EFFECTS Filed June 14, 1966 FIG.

LOW VOLTAGE TN PUT IN PUT WAVE OUTPUT WAVE SECTION GE NERATED VOLTAGES 36A ilk 38A FIG.

R o T N E V W HUGO W. SCHAFFT ATT YS United States Patent 3,397,328 VOLTAGE GENERATION UTILIZING PIEZOELECTRIC EFFECTS Hugo W. Schafit, Des Plaines, lll., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed June 14, 1966, Ser. No. 557,508 Claims. (Cl. 310--8.1)

This invention relates generally to piezoelectric devices, especially those used to generate periodic and aperiodic voltage waves.

Periodic voltage waves find applications in television deflection circuits, such as the well-known fiyback transformer generated deflection voltages. The use of transformers in generating such voltages is relatively expensive in that, inter alia, windings have to be carefully formed to insure the desired voltage characteristics are obtained. It is known that piezoelectric materials can be used to generate voltages corresponding to varying internal mechanical stresses, such as, shear and compressional shock waves. If such devices could be used for generation of high voltage waves, a simpler low cost periodic voltage generate signal can be provided.

Therefore, it is an object of this invention to provide a simple, low cost periodic or aperiodic voltage wave generator utilizing piezoelectric effects.

It is another object of this invention to provide a piezoelectric voltage generator which is mechanically actuated.

It is a further object of this invention to provide an electrically actuated piezoelectric voltage generator which provides two voltage output waves for each input voltage wave.

Referring now to the accompanying drawing:

FIG. 1 is a combined schematic and perspective view of an electrically actuated preferred embodiment of the subject invention, together with a modification providing an alternate embodiment;

FIG. 2 is a diagrammatic showing of waveforms used to describe the operation of the FIG. 1 embodiment;

FIG. 3 illustrates in a combined schematic and perspective view a mechanically actuated voltage wave generator;

FIG. 4 is an end view of the terminating end of the FIG. 3 embodiment.

According to this invention there is provided a piezoelectric material having two end portions separated by an elongated middle portion. The first end portion is stimulated to provide internal mechanical stresses, such as shock waves, which travel through the middle portion toward the second end portion. Attached to the middle portion are a plurality of spaced apart voltage sensing electrodes. A plurality of series connected rectifiers are respectively connected between adjacent spaced-apart electrodes. Alternating polarity voltage waves generate-d by a shock wave within the piezoelectric middle portion appears across each pair of adjacent electrodes. The respective rectifier shunts out one polarity of the piezoelectrically generated voltage wave and blocks the other polarity such as to store such other polarity voltage in the inherent capacitance of the piezoelectric material. The out-put voltage waveform is taken across opposite ends of the series circuit formed by the rectifiers. In the illustrated embodiments, due to the rectifier action the polarity of the output voltage waveform is always the same. Two embodiments are illustrated, one which electrically actuates the shock wave by an input electrical impulse and a second embodiment which uses a mechanical actuator for generating shock waves. Either embodiment may be used to produce periodic or aperiodic output voltages.

Referring now to FIG. 1 there is shown 'a bar 10 of piezoelectric material. A first end portion 12 has oppositely disposed input electrodes 14 and 16 for impressing an input electrical wave thereacross for piezoelectrically gen- "ice crating a shock wave which travels through the middli portion 18 toward the opposing end 24. A plurality of inter mediate electrodes 20 are disposed in spaced apart rela tionship along middle portion 18. Such electrodes may b bands plated around bar 10. The piezoelectrically gen erated voltages between adjacent spaced apart electrode 20 are summed together 'by a series circuit consisting o rectifiers 22 with the summed voltage taken between elec trode 16 and the most remote electrode 20A.

Rubber end portion 24A is attached to bar 10 immedi ately adjacent electrode 20A for dissipating by absorp tion receive-d shock waves traveling through the bar 10 This absorption prevents shock wave reflection and thereb' standing waves in the bar 10 which detract from voltag generation.

Operation of the FIG. 1 embodiment is best understoo with reference to the FIG. 2 illustrated waveforms. Inpu wave 26 having sharp rising wavefront 28 and shan falling trailing edge 30 is applied to the bar 10 across th electrodes 14 and 16. Wavefront 28 acts upon bar 10 t piezoelectrically generate shock wave 28A, shown in FIG l as a dotted line. Shock wave 28A traverses 'bar 10 fror end portion 12 to end 24. Input wave 26 actuates the FIG 1 assembly to provide two output voltage waves 32 an 34. Output waves 32 and '34 are the summation of th voltages generated between adjacent electrodes 20 whici are termed section generated voltages. Waves 32 an 34 are taken from the ends of the series circuit formed b rectifiers 22, that is, from electrodes 16 and 20A. Wave front 28 generated shock wave 28A piezoelectrically gen erates voltage wave 36 between each and every pair 0 adjacent electrodes 20. The respective diode 22 is forwar biased to current conduction to shunt or clamp out th generated voltage to limit the generated voltage to wav 36. Dotted line 38 indicates the opposing polarity of th generated voltage wave which is clamped out by actio of diode 22. Shock wave 28A generates a voltage havin the phase indicated by the combination of lines 36 and 3t Trailing edge 30 of input wave 26 piezoelectrically ger erates a voltage wave having the opposite phase, as indi cated in FIG. 2, by dotted line 38A appearing before wav 36A. The respective diode 22 again is forward biase to current conduction to clamp out the polarity of the gen erated voltage indicated by dotted line 38A. Voltage wav 34 begins to rise somewhat later with respect to trailin edge 30 than does output wave 32 with respect to risin front 28. The voltage humps 40 in the waves 32 and 3 correspond to the generated voltages in succeeding section 10A, 10B, 10C and 10D which individually correspond t voltage waves 36 and 36A. In each wave 32 and 34 ther are four voltage humps 40 each respectively correspond ing to and generated by the four illustrated sections 10A 10B, 10C and 10D of bar 10 formed between adjacer electrodes 20.

Spaced apart electrodes 20 preferably are metal band plated around bar 10. The portion of bar 10 covered b the bands 20 is inoperative to generate signals from th shock wave because of the shorting action of bands 21 Numeral 20B indicates an alternate form of spaced apa1 electrode in that it is a plate extending through and cross wise to the bar 10 length. B ands 20 are preferred becaus of simpler construction.

The shape of waves 32 and 34 may be varied by varyin the spacing between the electrodes 20. The closer the spat ing the lower the magnitude of the generated voltage there between and therefore the smaller the hump 40.

For optimum operation the spacing between adjacer electrodes 20 should be such that the shock wave portio therebetween, when the peak is centered therebetween, i as flat as possible, see FIG. 1 shock wave 28A.

Referring now to FIG. 1A there is shown a horsesho shaped piezoelectric bar 42 which corresponds in all de zils to the FIG. 1 embodiment except for the horseshoe rape. FIG. 1A is used only to illustrate that the particlar configuration of piezoelectric material may take any )rm whatsoever. It is to be further understood that the ivention is not limited to bar shaped materials. In testig the configuration of FIG. 1A a step-up in voltage of bout 6 to 1 was obtained by using a seven section piezolectric voltage wave generator.

Referring now to FIG. 3, there is shown a mechanically :tuated piezoelectric voltage wave generator. Bar 10C in re form of a solid cylinder is provided having spaced part output electrodes C in the form of annular bands lated circumferentially thereon for detecting the genrated voltages. A series circuit of rectifiers 22 are conected across the respective electrodes for providing an utput signal across the ends of the series circuit. A movble hammer 44 is placed in juxtaposition with end face 6 on the first ,portion of bar 100. Causing hammer 44 to like face 46 introduces a shock wave in bar 10C which perates to piezoelectrically generate voltages as described ith respect to FIG. 1. Operation of diodes 22 with repect to the generated voltages is identical to that dezribed with respect to FIG. 2 except that each time ham- 1er 44 strikes face 46 one output wave is generated.

Referring now to FIG. 4 there is shown an alternate lethod of dissipating the shock wave to avoid reflected 100k waves. Face 48 of the bar 10C second end portion, 5 seen by looking in the direction of arrow 48A, has a oughened end for dispersing the received shock wave in :veral directions. In this manner the shock wave is dis- .pated to avoid reflections.

What is claimed is:

1. For generating an electric voltage wave, in combinapiezoelectric means including a capacitance and having first and second end portions and a middle portion betwen the end portions,

means form introducing a mechanical stress into the piezoelectric means in said one end portion such that the stress travels through the middle portion to said second end portion,

a plurality of electrode means spaced apart along the middle portion such that a shock wave traveling therealong piezoelectrically generates electrical voltages between adjacent electrode means,

and a series electrical circuit interconnecting, the electrodes and including a plurality of rectifiers respectively connecting adjacent electrodes such that generated voltages between adjacent electrodes of a first polarity are shunted out while electrical voltages of a second plurality are blocked by the rectifiers and stored in capacitance of the piezoelectric means and the combination being such that the summation of the stored voltages appear across such series circuit.

2. The combination of claim 1 wherein the second end portion is formed so as to dissipate any mechanical stresses received thereby for preventing shock wave refiections.

3. The combination of claim 2 wherein said second end portion has a roughened face.

4. The combination of claim 2 wherein said second end portion has resilient material attached thereto.

5. The combination of claim 1 wherein the introducing means consists of a pair of electrodes for receiving electrical signals to impose a varied electric field across said first end portion for piezoelectrically introducing a mechanical stress into said piezoelectric means.

6. The combination of claim 5 wherein said spaced apart electrode means are metal bands disposed around the piezoelectric means.

7. The combination of claim 6 wherein said rectifier means are semiconductor diodes all poled in the same direction and respectively connected between adjacent bands.

8. The combination of claim 7 wherein the piezoelectric means is shaped such that the middle portion has a length along which the mechanical stress travels in a form of a shock wave which is substantially greater than any other dimension of said means.

9. The combination of claim 1 wherein the introducing means is a mechanical device which strikes said first end portion.

10. The combination of claim 9 wherein the spaced apart electrodes are metal bands disposed around the piezoelectric means.

References Cited UNITED STATES PATENTS 2,443,471 6/1948 Mason 333-72 2,806,155 9/1957 Rotkin 3108.1 2,921,134 1/1960 Greenspan 3l08.1 2,974,296 3/1961 Rosen 33372 2,975,354 3/1961 Rosen 3218 3,246,164 4/1966 Richmond 3108.1 3,271,622 9/1966 Malagodi 3108.1 3,334,307 8/1967 Blum 33330 J. D. MILLER, Primary Examiner. 

1. FOR GENERATING AN ELECTRIC VOLTAGE WAVE, IN COMBINATION: PIEZOELECTRIC MEANS INCLUDING A CAPACITANCE AND HAVING FIRST AND SECOND END PORTIONS AND A MIDDLE PORTION BETWEEN THE END PORTIONS, MEANS FORM INTRODUCING A MECHANICAL STRESS INTO THE PIEZOELECTRIC MEANS IN SAID ONE END PORTION SUCH THAT THE STRESS TRAVELS THROUGH THE MIDDLE PORTION TO SAID SECOND END PORTION, A PLURALITY OF ELECTRODE MEANS SPACED APART ALONG THE MIDDLE PORTION SUCH THAT A SHOCK WAVE TRAVELING THEREALONG PIEZOELECTRICALLY GENERATES ELECTRICAL VOLTAGES BETWEEN ADJACENT ELECTRODE MEANS, AND A SERIES ELECTRICAL CIRCUIT INTERCONNECTING THE ELECTRODES AND INCLUDING A PLURALITY OF RECTIFIERS RESPECTIVELY CONNECTING ADJACENT ELECTRODES SUCH THAT GENERATED VOLTAGES BETWEEN ADJACENT ELECTRODES OF A FIRST POLARITY ARE SHUNTED OUT WHILE ELECTRICAL VOLTAGES OF A SECOND PLURALITY ARE BLOCKED BY THE RECTIFIERS AND STORED IN CAPACITANCE OF THE PIEZOELECTRIC MEANS AND THE COMBINATION BEING SUCH THAT THE SUMMATION OF THE STORED VOLTAGES APPEAR ACROSS SUCH SERIES CIRCUIT. 